This invention relates to an automotive suspension system, and more particularly to a MacPherson strut type suspension system.
The MacPherson strut type suspension system includes a shock absorber having a piston-cylinder assembly and a coil spring. A cylinder in the shock absorber is coupled to an axle of an automobile, while a piston rod in the shock absorber is provided with an attaching portion to a body of an automobile. A coil spring is secured at its opposite ends to the piston rod and the cylinder, respectively, thereby absorbing a shock to be imposed on an automobile, when the automobile hits a bump or a hole in the road. In addition, the shock absorber absorbs vibration energy of a coil spring.
A resilient member is built in an attaching portion of the piston rod for preventing the transmission of a high frequency, small amplitude, light vibratory load (This will be referred to as a high frequency light vibratory load, hereinafter.) to an automotive body. For effectively preventing the transmission of such high frequency, light vibratory load, it is preferable to use a resilient member having a small elastic coefficient, i.e., a soft resilient member. However, with the aforesaid MacPherson strut type, the opposite ends of a coil spring are coupled to a piston rod and a cylinder, so that a low frequency, large amplitude, heavy load is applied to the resilient member built in the attaching portion. An increased displacement of the resilient member due to such a heavy vibratory load lowers operationability of an automobile, and accelerates deterioration of a resilient member. In addition, such a large displacement of a resilient member is not desirable from viewpoint of the space considerations in design, because a large space is required for preventing interference of the attaching portion with an automotive body.
Accordingly, this problem boils down to the fact that, for effectively preventing the transmission of a high frequency, light vibratory load or vibrations to an automotive body, as well as a large displacement of a resilient member due to a low frequency heavy vibratory load, it is preferable to provide a non-linear characteristic to a stress-strain relationship of the resilient member, i.e., a characteristic, in which the resilient member is susceptible to a light load but reluctantly causes an elastic deformation for a heavy load.
For this reason, there have been proposed various kinds of resilient-member-supporting constructions for an attaching portion of a prior art MacPherson strut type. However, these are too complicated in construction or result in the failure to isolate vibrations from an automotive body or to achieve desired operationability.